1. Field of the Invention
The invention relates to a building construction method for controlling attic moisture and improving the energy efficiency of a building by the installation of a breathable membrane in order to seal the attic space and provide an active air space between the attic and the roof deck.
2. Description of the Prior Art
In conventional building practices for construction of buildings having an attic space above the useful living space and below the roof, particularly buildings using wooden rafters and/or decking below the roof, the moisture level in the attic is typically controlled by ventilating the attic with air flow from the eaves of the building to the ridge vent at the highest point of the roof. As shown in FIG. 1, air is allowed to flow by means of convection from open spaces along the eaves (between the walls of the building and the bottom of the roof line) to the open space along the ridge(s) at the top of the roof, i.e., the ridge vent. This flow of air purges the attic of moisture before it can build up in the attic 2. Moisture commonly enters the attic from the living space in the form of vapor. Sources of moisture in the living space include human respiration, use of bathtubs and showers, cooking, houseplants, etc.
Typically, the attic 2 is open to the flow of air from the living space and from the exterior of the building surrounding the eaves. While this allows for good moisture control in the attic, it is often not energy-efficient since the living space 4 is not sealed and energy from the climate-controlled living space is permitted to leak to the exterior of the building through the ridge vent with the airflow.
Expandable foams have been used to insulate and seal the attic. The foams are sprayed under the roof decking and inside the roof rafters, or on the “floor” of the attic. While this can effectively seal the attic, this method does not prevent moisture from building up in the attic since the foams used are typically not breathable and do not permit air to flow through the attic, therefore this is not acceptable for many climates.
It would be desirable to provide a construction method that eliminates the exchange of air between the living space and the attic thereby providing good overall energy efficiency of the building, and that provides good control of moisture in the attic.